We report measurements and a model of gas flow through a helical duct of rectangular cross section. The measurements on helium, nitrogen, argon, and sulfur hexafluoride yielded molar flow rates from observations of the rate of rise of pressure in a known volume located downstream from the duct. The model yields flow rates based on the gas properties and the duct's entrance pressure, exit pressure, and temperature. It includes corrections for the gas's nonideal equation of state, the gas's expansion along the duct's length, the increase of kinetic energy near the duct's entrance, and slip. After adjusting only one parameter, the molar flow rate agrees with the model to within 0.2\% in the range of Reynolds number 0.08 < Re <40. Deviations of the molar flow rate from the model were caused by the duct's covature at larger Re. Their dependence on Re agrees with the pridicted value of the critical Dean number. The curvature effect inferred from numerical calculations by Targett et al. [AIChE J. 41, 1061 (1995)]explains the deviations to within 0.2% in the range 40< Re < 400 and to within 1% in the range 400 < Re <1000.
Citation: Aiche Journal
Issue: No. 2
Pub Type: Journals
curved duct, dean number, gas flow, laminar flow elements, rectangular duct